This invention relates to infusion pumps for administering fluid from a fluid source to a patient. More particularly, the invention relates to a highly portable, compact, pump having readily disposable and replaceable cassette-type pump and valve components, and capable of administering fluid to a patient at a flow rate which is substantially continuous and precisely controlled.
Previous infusion pumps for supplying fluids to patients can be classified generally as syringe type and peristaltic type. Among the syringe type infusion pumps are those shown in the following U.S. Pat. Nos.: 3,447,479; 3,701,345; 3,731,679; 3,739,943; 3,858,581; 3,901,231; 3,985,133; and 4,367,435. These syringe pumps all share the common characteristic of employing an electric motor to drive the plunger of a syringe so as to expel fluid therefrom at a controlled flow rate for administration to a patient. All syringe pumps likewise share the common problem of being incapable of providing a substantially continuous flow rate to the patient because of the necessity to interrupt delivery of the fluid while the plunger is being retracted to refill the syringe after it has been emptied. The resultant intermittent interruption of fluid flow to the patient during such refilling introduces a troublesome variable into flow rate planning, requiring higher than optimum flow rates during delivery of the fluid to make up for the intermittent interruptions in flow so that the time-averaged flow rate to the patient will be optimal. Unfortunately, the necessity for higher than optimal flow rates interspersed with interruptions thereof can cause both harmful excessive concentrations of infused fluids at some times, and harmful insufficient concentrations at other times The peristaltic type infusion pumps such as those shown in U.S. Pat. Nos. 3,73,930, 3,737,251 and 3,841,799, on the other hand, although providing substantially continuous flow, do not have the necessary accuracy of flow rate control provided by the syringe-type pumps and cannot therefore be used where a high degree of precision is required.
Another problem with prior infusion pump units is that their pumping and valving structures, even when provided in easily replaceable cassette form, lack the compactness and simplicity to provide a high degree of portability and versatility for both hospital and home use. Although some units, such as those shown in U.S. Pat. Nos. 3,456,648 and 3,994,294, employ simplified valving which utilize tube-deforming devices for selectively opening and closing fluid conduits, the means of packaging such simplified valving systems in a highly compact, replaceable cassette form have not been known.
Although highly accurate stepper motors have been used to control infusion pump flow rates, as exemplified by the aforementioned U.S. Pat. Nos. 3,736,930 and 3,985,133, the frequency control of pulses driving such motors does not provide adequate insurance that the commanded flow rate will actually occur, particularly under variable back pressure conditions. The same is true of pulsed, nonstepping motors utilized in pumps such as those shown in the aforementioned U.S. Pat. Nos. 3,858,581 and 4,367,435, where transient load conditions may likewise prevent the motor from moving in accordance with the drive pulses Moreover, the aforementioned pulsed electric motors do not have optimal energy efficiency characteristics which enable them to maximize the life of a battery power source, which would enhance their portability. Usually the drive pulses are of a constant duration which is longer than necessary to advance the motor the necessary amount against normal back pressures, thereby consuming excess power.
Finally, although a number of the prior infusion pump devices include occlusion detection systems, such as those shown for example in U.S. Pat. Nos. 3,731,679 and 3,985,133, such systems provide insufficient control over the likelihood that a partial occlusion, such as a partially obstructed or pinched fluid outlet, will disable the system. Accordingly, in some cases, disabling occlusions occur with excessive frequency, requiring excessive supervision and correction by an attendant.